Compounded thermal bimetal for ambient compensation



COMPOUNDED THERMAL BIMETAL FOR AMBIENT COMPENSATION Filed Dec. 8, 1958 INVENTOR. wu/444 #Awa/ mW/mf Arm/@WW United States Patent iiice Patented Nov. 13, 1962 The instant invention achieved ambient compensation 3,054,101 by providing a compounded thermal bimetal. Essen- COMPOUNDED THERMAL BIME'IAL FR AMBENT CMPENSATHGN William Harold Edmunds, Havertown, Pa., assigner to I -T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Dec. 8, 1958, Ser. No. 773,857

ZCIairns. (Cl. G-116) l The instant invention relates to circuit breakers in general and more particularly to a novel arrangement for an ambient temperature compensation means which will enable the thermal time delay tripping element of the circuit breaker to trip the circuit breaker at a constant predetermined current overload condition regardless of changes in ambient temperatures.

`Circuit; breakers, and more particularly molded case circuit breakers, are usually provided with a bimetal element which introduces a time delay in the interruption of the circuit breaker on the occurrence of an overload. Thus, for example, a circuit breakermay be calibrated at C. to carry rated current for an indelinite `length of time and 4to trip after a predetermined time interval if subjected to a predetermined overload current during that period. However, in the event that the ambient temperature of the circuit breaker environment goes above the lCalibrating temperature, for example to 50 C., the initial calibration is now in error. Hence, the circuit breaker will trip before the predetermined time delay expires. Thus, it is necessary to provide ambient temperature compensation means to insure that the circuit breaker will retain the characteristics 'of this initial cali-` bration regardless of changes in the ambient temperature.

The most important feature of amb-ient calibration is illustrated by considering a circuit lbreaker which is calibrated t0 carry a normal load current, for example 100 amperes at 25 C. indefinitely wit-hout tripping. That is, the 100 amperes represents a normal load which is not injurious to the electrical line or equipment protected by the circuit breaker. In the event that the ambient temperature goes above the 25 C. for example 50 C., the bimetal will deflect more at 50 C. than at 25 C. even though normal load current is flowing therethrough nnder both ambient temperature conditions. Hence, it is possible that this rise in ambient temperature will sufficiently deflect the bimetal to trip the circuit breaker thereby causing obvious abnormal interruption.

In single pole circuit breakers of the prior art, wherein the bimetal acts directly on the latch, ambient temperature compensation usually takes 4the form of an -auxiliary bimetal which deects in a direction opposite to the deiiection of the rnain circuit breaken bimetal and thereby adds a load to the main bimetal in the event lthat the ambient temperature is above the calibration temperature. Hence, even when the main bimetal is subjected to the high ambient temperature, it will neverthless overcome this additional load before the circuit breaker can trip.

In multi-pole molded circuit breakers of the prior` art, wherein a tripper bar is used, the latch is usually an integral part of the tripper Ibar with the deflection of the bimetal merely rotating the tripper bar to release the latch. In this type of arrangement the bimetal may even be spaced from the tripper bar or raised against a protrusion thereon. It is the degree of deflection of the bimetal which eventually results 4in tripping of the circuit breaker.

In this type of an arrangement, ambient compensation is achieved by placing a load on the tripper bar which is in opposition to the force exerted Ithereon by the main bimetal. This loading is `usually achieved by means of an auxiliary bimetal.- f v f tially this is a standard overcurrent bimetal on to which is brazed, or otherwise secured, an ambient compensating bimetal. The ambient compensating bimetal may be much lighter in construction than the overcurrent bimetal since the former is not required to carry load current. Further, the ambient compensating bimetal will have entirely different deflection characteristics than those ofthe overcurrent bimetal in that the former will be more sensitive to changes -in ambient temperature.

The ambient temperature compensating bimetal extends upwardly from the free end of the overcurrent bimetal and is arranged to deflect in a direction opposite to the deiiection of the overcurrent bimetal. It is the free end of the ambient temperature compensating bimetal which is engageable with the tripper bar for tripping of the circuit breaker.

As the ambient temperature rises the overcurrent bimetal deects in a direction which will cause tripping of the circuit breaker. However, at the same time the ambient compensating bimetal deflects in the opposite direction thereby maintaining the calibration of the circuit breaker. That is, the latch bite or the distance between the free end of the compounded thermal bimetal and the tripper bar may be maintained substantially uniform regardless of any changes in ambient temperature. It should be realized that the ambient temperature compensating bimetal will be effected to a limited extent by heat generated in the overcurrent bimetal by current flowing through the circuit breaker. This effect may readily be compensated for in the original calibration of the circuit breaker.

The compensated thermal bimetal according to the instant invention may be used in lany type of circuit breaker whether it be of a `directly or indirectly heated bimetal overcurrent construction. A compounded thermal bimetal has considerable advantages over ambient compensating devices of the prior art in that the compound thermal bimetal is a compact unit and the raw material of which the unit is comprised can be furnished in strip stock and blanked out to the desired conliguration.

Accordingly, a primary object of the instant invention is to prov-ide a circuit breaker having novel ambient compensating means.

Another object is to provide a compound thermal bimetal which is utilized as a temperature compensating device.

Still another object is to provide a circuit breaker in which the bimetal of the time delay tripping means comprises a compounded strip-like unit one portion of which is primarily detiected by heating caused by current flowing through the circuit breaker and another portion of which is primarily deliected by changes in ambient temperature with the deections of these two portions being in opposite directions thereby maintaining the calibration of the circuit breaker regardless of changes in ambient temperature.

These as well as other objects of the instant invention shall become readily apparent aft-er reading the following description of the accompanying drawings in which:

FIGURE 1 is a plan View of a circuit breaker, with the cover removed, which includes my novel compounded thermal bimetal.

IFIGURE 2 is a cross-section of a circuit breaker of WFIGURE l taken through the center phase thereof.

908 to I. C. Brumlield entitled Instantaneous Trip Cir-y cuit Breaker. Circuit breaker v is a three pole device including molded case consisting of a base v21, with suitable barrier formations 22.between the phases, and ai removable molded cover 23. A single operating mechanism 25, including manual operating handle 26, is utilized to achieve'simultaneous operation of all three phases.

The current path through the circuit breaker for each of the three phases A-C is identical, so for the sake of brevity only the current path of thecenter phase B will be described, it being understood that the current paths through the other phases A and C are identical to the current path through phase B. This current pathv comprises line terminal 27 which is secured to one end of formed strap 28 mounted to base 21 by means of screw 29 with stationary contact 30 Ibeing secured to the other end of strap 28. Movable contact 31 is mounted to one end of p ivoted contact arm 32 and is engageable with fixed contact 30. Braid 33 is secured to the other end of` contact ar-m 32 and extends to conductor 34 secured to base 21 by screw means 35. Compounded bimetal 100 extends upwardly from conductor 34 and at a point between the ends of compounded lbimetal 100 braid 36-is al'lixed. Braid 36'extends to load terminal 37 which is suitably secured toA base 21 to complete the current path.

`Operating mechanism includes an ar-m 38-which is pivotally mounted at 39l to rframe 40 and is operativelyy connected by means of spring 41 and sui-table linkagesr (not shown) to contactarm 32. Mechanism 25 further includes a klatchable cradle 42 pivoted at 41 to frame 40. Cradle 42 includes a latchtip 43 which is engageable with latch member 44, pivotally mounted at 45 to base 21. Latch member `44 in turn cooperates with common tripper bar 46 which extendstthroughall three phases A-C. lIn FIGURE 2, cradle 42 is latched inthe reset position awaiting operation of` handle 26 to the right with respect to FIGURE 2 to move contact 31 into engagement with contact 30.

Commontripper bar 46 includes a downward extension "47 in each phase to which a U-shaped ar-mature 48 is connected. Armature 48 cooperates with magnet 49, mounted near the bottom end of compounded bimetal 100, to provide an instantaneous tripping means forV circuit breaker 20. That is, upon the occurrence of a severe overload, armature 48 will be pivoted about end 50- thereof in a clockwise direction, with respect to FIGURE 3, thereby causing tripper bar 46 to rotate in a coun.- terclockwise direction, with respect to FIGURE 3, to free latch member `44 which in turnfrees latchv tip43 yand trips the circuit: breaker 20.

The time delay trip means comprises compoundedbimetal 100 which includes ay iirstl strip-like portion 101 designated the overcurrent bimetal and, extending-upwardly therefrom, a second portion 102 designated the ambient temperature compensating bimetal. Portions 101 andl102'are'rigidly secured to one another as by brazing. l K

VThelower end of compounded'bimetal 100V is iixedly secured by means of screw 35,While the upper or free end thereof isV provided with an adjusting screw 103,

passing through a threaded opening (not shown), and a lock nut 104. Common tripper bar 46 is provided in each of the phases with an upwardly projecting extension 53 which is engageableby end 105 of adjusting rscrew 103 when compounded bimetal 100y has been deflected due to the occurrence of overload conditions inthe particular phase. Heating of ambient compensating bimetalj 102 will cause itsupper end to dellecty to the right with-V respect to. FIGURE 3, .while heating of overcurrent bimetal 101 will causeitsupper end to; deflect to the left with ,respect to FIGURE 3.

'It Yis to be noted. that circuit current, while owing through overcurrent bimetal 101, does. not flow throughV ambient temperature. compensating bimetal 102.. Arn- 4 bientl compensating bimetal 102 is chosen to be extremely sensitive to changes in ambient temperature while overcurrent bimetal 101 is effected to a lesser degree inV changes in ambient temperature. Thus, the deflection of bimetal portion 102 will be due primarily to changes in ambient temperature while the deflection of bimetal portion 101 will be due primarily to heating thereof caused by circuit current passing therethrough.V

-If adjusting screw 103 is set in position while circuit breaker 20 is subjected to a Calibrating ambient temperature to establish a gap distance S lbetween screw tip 105 and tripper bar extension 53, a rise in ambient temperature while causing the upper end of overcurrent bimetal 101 to deilect to the left will at the same time cause the free end of ambient compensating bimetal 102 to deflect to the right thereby maintaining the gap distance S substantially constant.

Circuit current flowing through overcurrent bimetal 101 will cause heating and accompanying deection thereof which will move screw tip 105 to the left. Under current overload conditions this leftward detiection will cause screw tip 105 to engage tripper bar 46 counterclockwise with respect to FIGURE 3. Thus, latch member 44 is freed'of tripperbar 46 vand latchtip 43 is in turn freed of latch `member 44 which causesautomatic tripping ofv circuit breaker 20.

With ambient compensating bimetal 102 brazed to overcurrent bimetal 101 heating ofthe latter by circuit current will be conducted to the former to cause a deilection thereof. This may'befcompensated for in the calibration setting of adjusting screwy 103 together with aH suitable choice of bimetals which possess the requiredv characteristics which enables the deflection of portion 101 to complement the deflection of portion 102. Heat conductionbetween compounded bimetal portions 101 and 102 may be substantially eliminated by interposing a suitable heat insulator therebetween.

Itis also to bev notedthat ambienttemperature corny pensating bimetal 101 is made toV be much lighterinconture of the environment in which thecircuit breakerY is operating. Y

Although I have here described preferredv embodiment of my novel invention, many variations and modifications.

will now be apparentV to those skilled in the art, andv I therefore prefer to be limited, not by the specific disclosure herein, but only, by 'thel appending claims.

I claim: t

1. A time delay trip device for a circuit breaker comprising an elongated compounded bimetal includingaligned rst and second portions connected at one of the ends thereof; circuit connections at opposite endsof said lirst portion. whereby circuit current passes through said firstv with and'operation of a circuit breaker latch release mech-V anism upon predetermined circuit conditions; saidfcompounded bimetal being adjusted atan ambient calibration temperaturewhercby said means is positioned a predetermined-distance from a latch release mechanism; the.

second end of said second portion being dellectable in a iirst direction to effect tripping of said' circuitbreaker Y under predetermined. current overloadA conditions when v.said circuit breaker.A isY subjected to said` ambient cali;-

bration temperature; said second portion being, arranged,` f

upon arise in temperature thereof above Said ambient Calibrating temperature, to move said means in a second direction opposite to said rst direction; said trst portion being deflected primarily as a result of heat generated by current passing therethrough; said second portion being deilected primarily as a result of ambient teniperature; said iirst and second portions being constructed to complement one another whereby said time delay trip device will trip said circuit breaker at substantially said predetermined current overload conditions regardless of the ambient temperature to which said circuit breaker is subjected, said latch release mechanism including a tripper bar operable to trip said circuit breaker under control of said time delay trip device, said tripper bar being positioned a predetermined distance from said time delay trip device during normal operation, the deilection of said `first bimetal portion due to overload current being adapted 6 to urge said bimetal towards engagement with said tripper bar.

2. The device as set forth in claim l in which the means comprises an adjusting screw for varying the predetermined distance between the means and a latch release mechanism.

References Cited in the le of this patent UNITED STATES PATENTS 1,952,040 Frank et al Mar. 2G, 1934 2,179,811 Brosseau Nov. 4, 1939 2,336,408 Matthews Dec. 7, 1943 2,656,440 Dorfman Oct. 20, 1953 2,673,908 Brumiield Mar. 30, 1954 2,798,918 Gelzheiser July 9, 1957 2,813,167 Bingenheimer et al Nov. 12, 1957 2,847,532 Christensen et al Aug. l2, 1958 

